Worldwide carbonate rocks are occurring abundantly. These carbonate rocks are a major class of sedimentary rocks group. Carbonate are sedimentary rocks formed at (or near) the Earth surface by precipitation from solution at surface temperatures. The two broad categories are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3) and dolostone, which is composed of the mineral dolomite (Ca Mg (CO3)2). Dolomite is not a simple mineral; it can have a variety of origin, can form as a primary precipitate, a diagenetic replacement, or as a hydrothermal/metamorphic phase, all that it requires is permeability, a mechanism that facilitates fluid flow, and a sufficient supply of magnesium. Dolomite can also form in lakes, on or beneath the shallow seafloor, in zones of brine reflux, and in early to late burial settings. It may form from seawater, from continental waters, from the mixing of basinal brines, the mixing of hypersaline brine with seawater, or the mixing of seawater with meteoric water, or via the cooling of basinal brines. Potential fluid sources are seawater and subsurface fluid of marine and/or meteoric origin: and addition Mg could be released from high-Mg calcite and smectite clays. The only abundant source of Mg2+ ions for early diagenetic surface and near-surface dolomitization is seawater. Dolomitization also creates new crystals, with new rhomb growth following the dissolution of less stable precursors. Dolomitization model and formation depend on the source dolomitization site and lastly, there must exist a favorable condition for a chemical reaction. One particular type of dolomite which may be a cement or a replacement is baroque dolomite, also called 'saddle' or 'white sparry' dolomite and known to mineral collectors as pearl spar. It is characterized by a warped crystal lattice.
This article presents a description of Rare-earth elements (REE) which are a collection of seventeen metals that have distinctive and varied chemical, magnetic, and luminescent properties that make them strategically important in a number of high-technology industries. Consequently, the REE are increasingly becoming more attractive commodity targets for the mineral industry. This paper presents a comprehensive review of the distribution, geological characteristics and resources of Australia's major REE deposits. REE are generally associated with igneous, sedimentary, and metamorphic rocks in a wide range of geological environments. Elevated concentrations of these elements have been documented in various heavy-mineral sand deposits (beach, dune, marine tidal, and channel), carbonatite intrusions, (per)alkaline igneous rocks, iron-oxide breccia complexes, calc-silicate rocks (skarns), fluorapatite veins, pegmatites, phosphorites, fluviatile sandstones, unconformity-related uranium deposits, and lignites. The dissemination and deliberation of REE in these deposits are influenced by various rock-forming processes including enrichment in magmatic or hydrothermal fluids, separation into mineral species and precipitation, and subsequent redistribution and concentration through weathering and other surface processes. The lanthanide series of REE (lanthanum to lutetium) and yttrium show a close genetic and three-dimensional association with alkaline felsic igneous rocks, however, scandium in laterite profiles has a closer empathy with ultramafic/mafic igneous rocks. The highest level of the cataloguing comprises four general 'mineral-system association' categories, regolith, basinal, metamorphic, and magmatic, which in turn contain sixteen 'deposit type' members, namely: regolith-carbonatite-associated; ultramafic/mafic rock-associated; basinal-heavy mineral sand deposits in beach, high dune, offshore shallow marine tidal, and tidal environments; phosphorite; lignite; unconformity-related; metamorphic-calc-silicate; and magmatic-(per)alkaline rocks; carbonatite; pegmatite; skarn; apatite and/or fluorite veins; and iron-oxide breccia complex.
The sandstone units of the Early Cretaceous Lower Goru Formation are significant reservoir for gas, oil, and condensates in the Lower Indus Basin of Pakistan. Even though these sandstones are significant reservoir rocks for hydrocarbon exploration, the diagenetic controls on the reservoir properties of the sandstones are poorly documented. For effective exploration, production, and appraisal of a promising reservoir, the diagenesis and reservoir properties must be comprehensively analyzed first. For this study, core samples from depths of more than 3100 m from the KD-01 well within the central division of the basin have been studied. These sandstones were analyzed using petrographic, X-ray diffraction, and scanning electron microscopic analyses to unravel diagenetic impacts on reservoir properties of the sandstone. Medium to coarse-grained and well-sorted sandstone have been identified during petrographic study. The sandstone are categorized as arkose and lithic arkose. Principal diagenetic events which have resulted in changing the primary characters of the sandstones are compaction, cementation, dissolution, and mineral replacement. The observed diagenetic processes can be grouped into early, burial, and late diagenesis. Chlorite is the dominant diagenetic constituent that occurs as rims, coatings, and replacing grains. The early phase of coating of authigenic chlorite has preserved the primary porosity. The recrystallization of chlorite into chamosite has massively reduced the original pore space because of its bridging structure. The current study reveals that diagenetic processes have altered the original rock properties and reservoir characteristics of the Lower Goru sandstone. These preliminary outcomes of this study have great potential to improve the understanding of diagenetic process and their impact on reservoir properties of the Lower Goru sandstone in the Lower Indus Basin and adjoining areas.
Our research focuses on the reconstruction of turbidity paleocurrents of the Cilento Group in the Cilento area (southern Apennines, Italy). These deposits were formed in the wedge-top basin above the oceanic Ligurian Accretionary Complex, the early orogenic wedge of the southern Apennines. The Cilento Group succession, whose age ranges between the uppermost Burdigalian and lowermost Tortonian, consists of a thick pile of sandstones, conglomerates, marls and pelites grouped in two formations (Pollica and San Mauro Fms). We retrieved information on the turbidity current directions through sedimentary features such as flute and groove casts, flame structures and ripple marks. The aim of this study is to shed light on the early tectonic evolution of the southern Apennines by reconstructing the geometry of this basin, the source areas that fed it and the paleogeography of the central Mediterranean area in the Miocene. We analyzed 74 sites in both formations and collected 338 measurements of paleocurrent indicators. Because the succession was affected by severe thrusting and folding, every paleocurrent measurement was restored, reinstating the bedding in the horizontal attitude. Results indicate a complex pattern of turbidity current flow directions consistent with a basin model fed by a spectrum of sources, including recycled clasts from the Ligurian Accretionary Complex, Calabria–Peloritani Terrane and the Apennine Platform units and volcaniclastics from the synorogenic volcanoes located in the Sardinia block.
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